With its rapid development, the LCD technology has been widely used in all aspects of daily life. There have been considerable markets for LCD panels in information household appliances, such as liquid crystal screens, portable audio-video products of consumption type, mobile phones, liquid crystal televisions and the like, not to mention its traditional application to notebook computers (NB). Although the picture quality of LCD screens is closer to that of the completely developed cathode-ray tube (CRT) screens, there are still some problems of visual angle, contrast, display uniformity and the like in LCD screens, which need to be improved. Furthermore, in regard to the applications concerning high-density, highly refined and large-sized products, such as liquid crystal televisions, there are also problems desired to be solved with response speed and color reproducibility in LCD screens. The techniques concerning the control of liquid crystal alignment and the alignment films are closely related to the above-mentioned problems in liquid crystal panels. Therefore, manufacturing and controlling the alignment films are quite important.
FIG. 1 shows a schematic diagram of a cross section of a liquid crystal display 10 in the prior art, wherein alignment films 7 are located between a liquid crystal 6 and transparent electrodes 3 and 4. The importance of the alignment films 7 is due to the working principle of the liquid crystal display 10. The liquid crystal 6 can be applied to a screen, as the dielectric constants of the liquid crystal 6 in the direction parallel with the molecules and those in the direction perpendicular to the molecules are different, whereby the liquid crystal can be driven through an electric field. On the other hand, the liquid crystal also has a refractive index varied according to the orientations of the molecules, i.e. exhibits a birefringence effect, which will change the polarizing direction of polarized light. A strong anchoring strength exists on the interfaces between the liquid crystal 6 and the alignment films 7, and the liquid crystal 6 is restored to its original arrangement by means of elasticity, i.e. restoring force, after the electric field is turned off. Therefore, as is clearly evident, the liquid crystal 6 cannot function in the absence of the alignment films 7.
The LCD panel manufacturing technology is becoming increasingly mature. With reference to FIG. 1, at present, an active TFT array substrate 1 with patterns and a color filter (CF) substrate 2 are generally first manufactured. An alignment film 7 is then coated on the inner surface of each of the active TFT array substrate 1 and the color filter substrate 2. After heating and baking of the alignment films 7, the TFT array substrate 1 and the color filter substrate 2 are adhered together with a sealant 5, and liquid crystal 6 is filled into the space encompassed by the sealant 5, the TFT array substrate 1 and the color filter substrate 2. The alignment films 7 are used for the alignment of the liquid crystal 6, thus if the alignment films 7 are not heated uniformly during the baking, the alignment of the liquid crystal 6 would be disrupted, which ultimately leads to a Mura phenomenon on display panels.
FIG. 2 schematically shows a glass substrate 11 located in a baking device. FIG. 3 shows a front view of a baking device 20 for liquid crystal alignment films in the prior art. With reference to FIG. 2 and FIG. 3, a commonly-used prebake oven 20 performs heating with a heating table 15 provided with openings. Positions 17 on the treated glass substrate 11, to which the openings of the heating table 15 correspond respectively, are indicated by circles in FIG. 2. Lift pins 13 pass through the openings, and the lift pins 13 can move between a stretching position and a retracting position to support the treated glass substrate 11, which is coated with the alignment films. The glass substrate 11 is fetched and fed by a manipulator and is then processed with the ascending and descending of the lift pins 13.
The lift pins 13 are situated in their retracting positions in FIG. 3. When the lift pins 13 are located at the retracting positions and the glass substrate 11 is being processed, due to the openings on the heating table 15, air streams 14 can reach the bottom side surface of the glass substrate 11, i.e. the side surface of the glass substrate 11 facing the heating table 15, through the openings, which will cause temperature difference between the openings 17 and areas without such openings on the glass substrate 11. Inevitably, most of the openings through which the lift pins 13 can pass may correspond to display areas 12 on the glass substrate 11, which causes non-uniform heating of the alignment films and thus the Mura phenomenon on the whole display panel.